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BACKGROUND: Irritable bowel syndrome (IBS) is a complex condition with multiple factors contributing to its aetiology and pathophysiology. Aetiologically these include genetics, life-time events and environment, and physiologically, changes in motility, central processing, visceral sensitivity, immunity, epithelial permeability and gastrointestinal microflora. Such complexity means there is currently no specific reliable biomarker for IBS, and thus IBS continues to be diagnosed and classified according to symptom based criteria, the Rome Criteria. Carefully phenotyping and characterisation of a 'large' pool of IBS patients across Europe and even the world however, might help identify sub-populations with accuracy and consistency. This will not only aid future research but improve tailoring of treatment and health care of IBS patients. PURPOSE: The aim of this position paper is to discuss the requirements necessary to standardize the process of selecting and phenotyping IBS patients and how to organise the collection and storage of patient information/samples in such a large multi-centre pan European/global study. We include information on general demographics, gastrointestinal symptom assessment, psychological factors, quality of life, physiological evaluation, genetic/epigenetic and microbiota analysis, biopsy/blood sampling, together with discussion on the organisational, ethical and language issues associated with implementing such a study. The proposed approach and documents selected to be used in such a study was the result of a thoughtful and thorough four-year dialogue amongst experts associated with the European COST action BM1106 GENIEUR (www.GENIEUR.eu).

ABSTRACT:
Irritable bowel syndrome (IBS) is a functional gastrointestinal disease with a high population prevalence. The disorder can be debilitating in some patients, whereas others may have mild or moderate symptoms. The most important single risk factors are female sex, younger age and preceding gastrointestinal infections. Clinical symptoms of IBS include abdominal pain or discomfort, stool irregularities and bloating, as well as other somatic, visceral and psychiatric comorbidities. Currently, the diagnosis of IBS is based on symptoms and the exclusion of other organic diseases, and therapy includes drug treatment of the predominant symptoms, nutrition and psychotherapy. Although the underlying pathogenesis is far from understood, aetiological factors include increased epithelial hyperpermeability, dysbiosis, inflammation, visceral hypersensitivity, epigenetics and genetics, and altered brain-gut interactions. IBS considerably affects quality of life and imposes a profound burden on patients, physicians and the health-care system. The past decade has seen remarkable progress in our understanding of functional bowel disorders such as IBS that will be summarized in this Primer.

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IBS is the most prevalent functional gastrointestinal disorder and phenotypically characterized by chronic abdominal discomfort, pain and altered defecation patterns. The pathophysiology of IBS is multifactorial, albeit with a substantial genetic component. To date, studies using various methodologies, ranging from family and twin studies to candidate gene approaches and genome-wide association studies, have identified several genetic variants in the context of IBS. Yet, despite enlarged sample sizes, increased statistical power and meta-analyses in the past 7 years, positive associations are still scarce and/or have not been reproduced. In addition, epigenetic and pharmacogenetic approaches remain in their infancy. A major hurdle is the lack of large homogenized case-control cohorts recruited according to standardized and harmonized criteria. The COST Action BM1106 GENIEUR (GENes in Irritable Bowel Syndrome Research Network EURope) has been established to address these obstacles. In this Review, the (epi)genetic working group of GENIEUR reports on the current state-of-the-art in the field, highlights fundamental flaws and pitfalls in current IBS (epi)genetic research and provides a vision on how to address and improve (epi)genetic approaches in this complex disorder in the future.

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Serotonin type 3 (5-HT(3)) receptors are ligand-gated ion channels built by five subunits of diverse composition. In humans, five subunits exist (5-HT3A-E) which are encoded by the genes HTR3A-E and are expressed in various isoforms. Recently, the importance of factors influencing receptor expression became clear, such as chaperones and microRNAs. Owing to their expression profile and physiological functions, 5-HT(3) receptors have been implicated in irritable bowel syndrome (IBS) and psychiatric disorders. Interestingly, HTR3 variants have now been shown to be associated with these conditions. This underlines the potential of 5-HT(3) receptors as therapeutic targets and may enable personalised therapies in the future.

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OBJECTIVE: Different forms of psychotherapeutic treatments have been proven effective in irritable bowel syndrome (IBS), but disorder-oriented and integrative concepts are still rare. Therefore, we implemented and evaluated an integrative group therapeutic concept within an interdisciplinary tertiary care clinic for functional gastrointestinal disorders (FGIDs). AIMS: present our integrative group concept, assess feasibility issues, and evaluate efficacy. METHODS: A pilot-RCT with a randomized controlled wait-listed group design was conducted. The treatment concept was a disorder-oriented multicomponent group therapy (12 90-min weekly sessions) integrating interactive psychoeducation, gut-directed hypnotherapy, and open group phases. All patients received enhanced medical care and completed a short online diary as an active wait-listed control condition. INCLUSION CRITERIA: refractory IBS diagnosed as somatoform autonomic dysfunction of the lower gastrointestinal tract (SAD). PRIMARY OUTCOME: IBS symptom severity (IBS-SSS). RESULTS: Of 294 patients, 220 had IBS (ROME III), 144 were diagnosed as SAD (ICD-10), 51 were eligible regarding inclusion/exclusion criteria, and 30 consented to participate (group intervention: n=16, wait-listed control condition: n=14). Only 1 patient dropped out. Intention-to-treat-analysis with repeated-measures mixed ANOVA showed that the group intervention was not significantly superior to the wait-listed control condition. Nevertheless, the calculated effect size for the between-group difference in IBS-SSS at the end of treatment (post) was moderate (d=0.539). CONCLUSION: Our disorder-oriented integrative group intervention for IBS proved to be acceptable and feasible in an interdisciplinary tertiary care setting. There is promise in this intervention, but a larger RCT may be needed to investigate efficacy.

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BACKGROUND: The calcium-sensing receptor (CaSR) is a calcium (Ca(2+)) sensitive G protein-coupled receptor implicated in various biological processes. In particular, it regulates Ca(2+)/Mg(2+)- homeostasis and senses interstitial Ca(2+) levels and thereby controls downstream signalling cascades. Due to its expression in the gut epithelium, the enteric nervous system and smooth muscles and its key function in regulation and coordination of muscular contraction and secretion, it represents an excellent candidate gene to be investigated in the pathophysiology of irritable bowel syndrome (IBS). Disturbed CaSR structure and function may impact gastrointestinal regulation of muscular contraction, neuronal excitation and secretion and consequently contribute to symptoms seen in IBS, such as disordered defecation as well as disturbed gut motility and visceral sensitivity. METHODS: We have therefore genotyped the functional CASR SNP rs1801725 in three case control samples from the UK, Belgium and the USA. RESULTS: Genotype frequencies showed no association in the three genotyped case-control samples, neither with IBS nor with IBS subtypes. CONCLUSIONS: Although we could not associate the SNP to any of the established bowel symptom based IBS subtypes we cannot rule out association to altered Ca(2+) levels and disturbed secretion and gut motility which were unfortunately not assessed in the patients genotyped. This underlines the necessity of a more detailed phenotyping of IBS patients and control individuals in future studies.

Orand, Alexa / Gupta, Arpana / Shih, Wendy / Presson, Angela P / Hammer, Christian / Niesler, Beate / Heendeniya, Nuwanthi / Mayer, Emeran A / Chang, Lin. ·Oppenheimer Center for the Neurobiology of Stress, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America. · Department of Biostatistics, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America. · Department of Biostatistics, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, United States of America; Division of Epidemiology, Department of Internal Medicine, University of Utah, Salt Lake City, Utah, United States of America. · Institute of Human Genetics, Department of Human Molecular Genetics, University of Heidelberg, Heidelberg, Germany. ·PLoS One · Pubmed #26288143.

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BACKGROUND: Genetic and environmental factors contribute to the pathophysiology of irritable bowel syndrome (IBS). In particular, early adverse life events (EALs) and the catecholaminergic system have been implicated. AIMS: To investigate whether catecholaminergic SNPs with or without interacting with EALs are associated with: 1) a diagnosis of IBS, 2) IBS symptoms and 3) morphological alterations in brain regions associated with somatosensory, viscerosensory, and interoceptive processes. METHODS: In 277 IBS and 382 healthy control subjects (HCs), 11 SNPs in genes of the catecholaminergic signaling pathway were genotyped. A subset (121 IBS, 209 HCs) underwent structural brain imaging (magnetic resonance imaging [MRI]). Logistic and linear regressions evaluated each SNP separately and their interactions with EALs in predicting IBS and GI symptom severity, respectively. General linear models determined grey matter (GM) alterations from the SNPs and EALs that were predictive of IBS. RESULTS: 1) DIAGNOSIS: There were no statistically significant associations between the SNPs and IBS status with or without the interaction with EAL after adjusting for multiple comparisons. 2) SYMPTOMS: GI symptom severity was associated with ADRA1D rs1556832 (P = 0.010). 3) Brain morphometry: In IBS, the homozygous genotype of the major ADRA1D allele was associated with GM increases in somatosensory regions (FDR q = 0.022), left precentral gyrus (q = 0.045), and right hippocampus (q = 0.009). In individuals with increasing sexual abuse scores, the ADRAβ2 SNP was associated with GM changes in the left posterior insula (q = 0.004) and left putamen volume (q = 0.029). CONCLUSION: In IBS, catecholaminergic SNPs are associated with symptom severity and morphological changes in brain regions concerned with sensory processing and modulation and affect regulation. Thus, certain adrenergic receptor genes may facilitate or worsen IBS symptoms.

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BACKGROUND: To date, genetic-association studies of single nucleotide polymorphisms (SNP) in selected candidate genes with the symptom phenotype of irritable bowel syndrome (IBS) have typically involved hundreds to 2000 patients. SNPs in immune-related genes, such as cytokine and cytokine receptor encoding genes, have been reported to associate with IBS risk. METHODS: We conducted two independent case-control studies on 16 SNPs in IL1R1, IL4, IL6, IL8, IL10, IL23R, TNFA, and TNFSF15, one from the UK (194 patients and 92 healthy volunteers) and one from the USA (137 patients and 96 healthy volunteers). The main aim was to examine the relationship between inherited immunological diversity and IBS risk in a meta-analysis which included 12 additional, earlier studies. The meta-analysis comprised a total of 2894 patients (839 IBS-C, 1073 IBS-D, 502 IBS-M), and 3138 healthy volunteers with self-reported Caucasian ancestry. KEY RESULTS: The association of SNP rs4263839 (TNFSF15) was investigated in four studies and confirmed in the meta-analysis: IBS (OR 1.19, 95% CI 1.08-1.31), and IBS-C (OR 1.24, 95% CI 1.08-1.42). No additional SNPs residing in immunogenes associated with IBS symptom phenotypes. CONCLUSIONS & INFERENCES: Our meta-analysis could not confirm a major role of most investigated SNPs, but a moderate association between rs4263839 TNFSF15 and IBS, in particular IBS-C. The analysis emphasizes the importance of definition and phenotype homogeneity, adequate study size and representativeness of the patient and control collective.

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OBJECTIVE: IBS shows genetic predisposition, but adequately powered gene-hunting efforts have been scarce so far. We sought to identify true IBS genetic risk factors by means of genome-wide association (GWA) and independent replication studies. DESIGN: We conducted a GWA study (GWAS) of IBS in a general population sample of 11,326 Swedish twins. IBS cases (N=534) and asymptomatic controls (N=4932) were identified based on questionnaire data. Suggestive association signals were followed-up in 3511 individuals from six case-control cohorts. We sought genotype-gene expression correlations through single nucleotide polymorphism (SNP)-expression quantitative trait loci interactions testing, and performed in silico prediction of gene function. We compared candidate gene expression by real-time qPCR in rectal mucosal biopsies of patients with IBS and controls. RESULTS: One locus at 7p22.1, which includes the genes KDELR2 (KDEL endoplasmic reticulum protein retention receptor 2) and GRID2IP (glutamate receptor, ionotropic, delta 2 (Grid2) interacting protein), showed consistent IBS risk effects in the index GWAS and all replication cohorts and reached p=9.31×10(-6) in a meta-analysis of all datasets. Several SNPs in this region are associated with cis effects on KDELR2 expression, and a trend for increased mucosal KDLER2 mRNA expression was observed in IBS cases compared with controls. CONCLUSIONS: Our results demonstrate that general population-based studies combined with analyses of patient cohorts provide good opportunities for gene discovery in IBS. The 7p22.1 and other risk signals detected in this study constitute a good starting platform for hypothesis testing in future functional investigations.

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BACKGROUND: Impaired 5-HT3 receptor function is likely involved in the pathogenesis of functional gastrointestinal disorders (FGID) and 5-HT3 receptor antagonists are effective treatments for chemotherapy-induced nausea and vomiting (CINV) and irritable bowel syndrome (IBS). The monoterpene alcohol menthol and the aporphine alkaloid boldine combat symptoms of gastrointestinal diseases; both interact with other members of the Cys-loop ligand-gated ion channel family and may therefore also act on 5-HT3 receptors. METHODS: The impact of boldine and menthol on human recombinant homomeric 5-HT3 A- and heteromeric 5-HT3 AB receptors in HEK293 cells was determined by radioligand binding, a luminescence-based Ca(2+) assay, and a membrane potential assay. 5-HT3 protein and mRNA expression was assessed in human colon tissue. KEY RESULTS: Boldine and menthol inhibited the 5-HT-induced activation of 5-HT3 receptors in the low and middle micromolar range, respectively. Boldine was a competitive antagonist of both receptors being 6.5- to 10-fold more potent at 5-HT3 A- vs 5-HT3 AB receptors. Menthol non-competitively and stereoselectively inhibited both receptors: In contrast to (+)-menthol, (-)-menthol was significantly more potent toward 5-HT3 A- vs 5-HT3 AB receptors. We show co-expression of 5-HT3A and 5-HT3B subunits in the human gut epithelium, the lamina propria, the myenteric plexus, and the muscular cell layer. CONCLUSIONS & INFERENCES: The demonstrated 5-HT3 inhibitory effects may be relevant for boldine's and menthol's alleviating properties on FGID and may encourage clinical studies with the compounds or the plant extracts for CINV and IBS treatment. The found receptor-discriminative properties make boldine and (-)-menthol to potentially useful tools for analyzing structural differences between these receptor subtypes.

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BACKGROUND & AIMS: 5-Hydroxytryptamine (5-HT)3 receptor (5-HT3R) antagonists are effective in treating patients with irritable bowel syndrome (IBS) and have anxiolytic effects. Their therapeutic effects are related, in part, to reducing amygdala engagement during expected visceral pain. A single nucleotide polymorphism in HTR3A, c.-42C>T;(C178T; rs1062613), is associated with altered reactivity of the amygdala during emotional face processing in healthy subjects (controls). We evaluated the influence of this single nucleotide polymorphism on amygdala reactivity to emotional faces and nonemotional stimuli in female patients with IBS and controls. METHODS: We measured brain responses during an affect-matching paradigm in 54 women (26 with IBS, 29 controls) using functional magnetic resonance imaging. We examined associations between HTR3A c.-42C>T genotype (C/C vs T carrier) and responses in amygdala and other regions of brain that expressed high levels of 5-HT3R. RESULTS: The C/C genotype was associated with greater anxiety symptoms in patients with IBS and controls and increased activation of the amygdala under emotional and nonemotional conditions. Among patients with IBS, C/C genotype was associated with greater symptom ratings. A subset of IBS patients with the C/C genotype had increased amygdala responses to nonemotional stimuli, compared with other subjects with C/C genotype. CONCLUSIONS: Regardless of diagnosis, the C/C genotype of the c.-42C>T polymorphism in HTR3A, compared with T carrier status, is associated with increased anxiety and amygdala responsiveness during emotional and nonemotional tasks. This polymorphism was associated with severity of IBS symptoms. Although this genotype is not sufficient for diagnosis of IBS, it is associated with severity of symptoms.